HTML/CSS Making a textbox with text that is grayed out, and disappears when I click to enter info, how?

Chrome, Firefox, IE10 and Safari support the html5 placeholder attribute

<input type="text" placeholder="First Name:" />

In order to get a more cross browser solution you'll need to use some javascript, there are plenty of pre-made solutions out there, though I don't know any off the top of my head.

http://www.w3schools.com/tags/att_input_placeholder.asp

This answer illustrates a pre-HTML5 approach. Please take a look at Psytronic's answer for a modern solution using the placeholder attribute.

HTML:

<input type="text" name="firstname" title="First Name" style="color:#888;" 
    value="First Name" onfocus="inputFocus(this)" onblur="inputBlur(this)" />

JavaScript:

function inputFocus(i) {
    if (i.value == i.defaultValue) { i.value = ""; i.style.color = "#000"; }
}
function inputBlur(i) {
    if (i.value == "") { i.value = i.defaultValue; i.style.color = "#888"; }
}